1. Field
Example embodiments relate to light-sensing circuits, methods of operating the light-sensing circuits, and light-sensing apparatuses including the light-sensing circuits, and more particularly, to light-sensing circuits including a light-sensitive oxide semiconductor transistor as a light-sensing device, methods of operating the light-sensing circuits, and light-sensing apparatuses, such as an optical touch panel or an image acquisition apparatus, including the light-sensing circuits.
2. Description of the Related Art
Touch screens are apparatuses that allow input data to be directly input on a display screen in such a way that when, for example, a person's finger or a pen or similar is brought into contact at a particular position of the display screen, the contact position is identified, and then a corresponding process is performed by software. To do this, touch screens further include a touch panel that is attached to a general display panel to perform the function described above. Examples of the touch panel include a resistive overlay-type touch panel, a capacitive overlay-type touch panel, a surface acoustic wave (SAW)-type touch panel, an infrared beam-type touch panel, and a piezo electric-type touch panel or the like. Such touch screens have alternative input devices such as a keyboard or a mouse, and are used in a variety of fields.
However, widely used touch panels operate only when a person's finger or pen is brought into direct contact with the panels. Accordingly, when resistive overlay-type touch panels, which are the most widely used among the touch panels, are used, an upper or lower conductive layer may be damaged due to external pressure. Moreover, resistive overlay-type touch panels may be used only in small screens having a size of 10 inches or less. Large touch panels for large screens fail to perform a sufficient function due to a line resistance and a parasitic resistance. Thus, currently, touch panels are used in a small-size or middle-size display of, for example, a general desktop computer, a notebook computer, or a portable device, such as a mobile phone or a navigation device. Thus, the touch panels are not suitable when a large display is used and a distance between a user and a display is increased.
Recently, optical touch panels that perform the same function as the touch panels by sensing light instead of the contact with a person's finger or a pen have been introduced. In an optical touch panels, a small light-sensing device is used. Meanwhile, an image acquisition apparatus, such as a complimentary metal oxide semiconductor (CMOS) or a charge-coupled device (CCD), also requires a light-sensing device that is capable of sensing light in order to acquire an image. An example of a generally used light-sensing device is a photodiode having as a basic structure a PN junction of a semiconductor such as silicon.
However, a silicon photodiode does not have a sufficient light-derived current change. Thus, charges, which are generated in a photodiode when light is irradiated, are accumulated in a capacitor for a certain period of time, and then a signal corresponding to the intensity of light is generated based on the intensity of charges accumulated in the capacitor. When a capacitor is used as described above, however, the larger an optical touch panel or image acquisition device is, the higher parasitic capacitance. Thus, large optical touch panels or image acquisition devices may be difficult to manufacture.